The present invention relates to a holding fixture, and more particularly to a holding fixture capable of holding predetermined contoured workpieces such as aircraft skin panels.
In manufacturing processes the same workpiece often must undergo several machining operations such as drilling, boring, routing, etc. It is desirable to rigidly fix a contoured workpiece in one position and conduct several machining operations. Further, it is desirable to perform several machining operations in the same location or in a manufacturing "cell" using the same set of work tools for a succession of different shaped workpieces. A workpiece such as an aircraft skin panel must be rigidly fixtured in its correct contour and held during processing. In order to maintain maximum productivity of the manufacturing cell, a change over to the next panel of different curvature should be accomplished as rapidly as possible. Such centrally located processes in a manufacturing cell can greatly reduce manufacturing costs by saving time, increasing efficiency and productivity, reducing manpower requirements, and avoiding machine and retooling expenditures.
Holding fixtures capable of accommodating various contoured workpieces are known in the prior art. For example, U.S. Pat. No. 4,894,903 discloses an aircraft wing skin panel assembly jig using a set of headers, releasably attached to a frame, which corresponds to a particular wing skin panel. A new set of headers can be attached to the frame to accommodate a different wing skin panel. This process however is labor intensive and may not be practical for many manufacturing processes.
U.S. Pat. No. 4,946,149 discloses a programmable working tool bed having a contoured platen containing several retractable workpiece stops, and a plurality of pop-up suction cups to secure workpieces. Similarly, U.S. Pat. No. 4,723,766 discloses a programmable spaced array of retractable vacuum pods supported within a work table wherein the particular known set of vacuum pods is raised and activated to hold a predetermined workpiece.
In addition, U.S. Pat. No. 4,684,113 discloses a matrix of vacuum cup holders housed in a horizontal support table, wherein each cup is attached to a servo actuator and controlled by a computer. This type of holding fixture is sometimes referred to as "a bed of nails" fixture. Although a bed of nails fixture can accommodate a large variety of contours and the contours can be easily altered, each servo actuator is fairly expensive; larger manufacturing applications of this technology often require more than 100 such actuators. The result is a very expensive holding fixture.